Stimulating wells with liquid explosives

ABSTRACT

This is a method for increasing the permeability of underground formations adjacent a well bore by explosive fracturing. This invention relates especially to a special method of placing the liquid explosive in the well. It includes setting a plugged packer in the well just above the formation to be stimulated. A tubing string is run in the well with the lower end just above the plugged packer. The selected amount of liquid explosive is then forced into the tubing string. After this, the tubing string is inserted in the packer and the plug of the packer is removed. The explosive is then forced downward into the well bore. The packer is replugged, tubing is removed and the well bore stemmed. The detonation is then effected.

United States Patent Inventors Clarence R. Fast;

George C. Howard; Riley F. Farris, all of Tulsa, Okla. Appl. No. 30,751Filed Apr. 22, 1970 Patented Dec. 7, 1971 Assignee Amoco ProductionCompany Tulsa, Okla.

STIMULATING WELLS WlTll LIQUID EXPLOSIVES 15 Claims, 6 Drawing Figs.

US. Cl

Int. Cl

References Cited UNITED STATES PATENTS 2,316,596 4/1943 Kennedy2,707,436 5/1955 McCool E2lb 43/26 Field of Search 3,561,532 2/1971Fletcher et al Q: 166/299 Primary Examiner-Stephen J. NovosadAttorneys-Paul F. Hawley and John D. Gassett ABSTRACT: This is a methodfor increasing the permeability of underground formations adjacent awell bore by explosive fracturing. This invention relates especially toa special method of placing the liquid explosive in the well. Itincludes setting a plugged packer in the well just. above the formationto be stimulated. A tubing string is run in the well with the lower endjust above the plugged packer. The selected amount of liquid explosiveis then forced into the tubing string. After this, the tubing string isinserted in the packer and the plug of the packer is removed. Theexplosive is then forced downward into the well bore. The packer isreplugged, tubing is removed and the well bore stemmed. The detonationis then effected.

NITROGEN 36 PATENTEDnEc "(I971 3.625285 SHEET 1 OF 3 CLARENCE R. FASTGEORGE C. HOWARD RILEY F. FARRIS INVENTORS ATTORNEY PATENTEDBEB 1m3.625285 SHEET 2 BF 3 NITROGEN 36 EXPLOSIVE 34 27?:- p 54 52 5O 2 ISORBING SOLVENT 64 72 WATER /62 32 7O 4-1;;3 CLARENCE R. FAST GEORGE c.HOWARD --i:'- r"* RILEY F. FARRIS 5 1 INVENTORS ATTORNEY.

PATENTED DEC 7 :sn

SHEET 3 [1F 3 04 0 2. w 992 9 w x H// \v x my /r \4w X f. C 5 l 6 4 3 28 8 CLARENCE R. FAST GEORGE C. HOWARD RILEY F. FARRIS INVENTORS BY 4. y;A r

ATTORNEY.

STIMULATING WELLS WITI-I LIQUID EXPLOSIVES BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to a methodof increasing the permeability in a formation adjacent an oil and gaswell which penetrates therethrough. It relates especially to a system ofplacing a liquid explosive in the well, subsequent detonation, andcleaning out operations to place the well on production.

2. Setting of the Invention Many oil and gas wells are drilled intopetroleum-bearing formations which have low permeability. That is, theformations are of a character that is difficult for the oil to berecovered; in other words, the formation is very reluctant to give upits petroleum. When such formation rocks are encountered, it becomesnecessary to resort to one or more means to increase the permeability.One means which has been quite successful is the hydraulic fracturingtechnique. In this system a special hydraulic fracturing fluid isinjected through the well bore adjacent to the formation. Fluid iscontinued to be pumped into the well bore so as to increase the pressureto the point where the formation is fractured. When this fracturingoccurs there are usually propping agents leftin the fractures so thatthe fractures will remain open, forming new paths for the oil to flowfrom the rock into the well bore. Frequently, this type stimulation doesnot result in desired production increases as it does not reach theunfractured matrix of the formation. Although hydraulic fracturing haspermitted the production of billions of barrels of oil not heretoforerecovered, there is still some room for improvement.

BRIEF DESCRIPTION OF THE INVENTION A drillable packer is set in the wellbore just above the formation to be fractured. The ordinary passagethrough the packer is plugged by a shear plug set in a shear plug subbeneath the packer. A string of tubing is run in the well with the lowerend just above the packer. A liquid explosive is then forced into thetubing string until the desired amount is injected therein. At the sametime liquid is removed from the annulus of the well. Next the tubing isconnected into the packer and pressure applied to the liquid explosiveto force the shear plug through the shear plug sub. The liquid explosiveis then forced on downwardly into a well below the packer. The packer isreplugged, the tubing removed and the well stemmed. After such stemming,the liquid explosive is detonated. The well is subsequently cleaned outand placed on production.

DESCRIPTION OF THE DRAWINGS Various objectives and a betterunderstanding of the invention can be had from the following descriptiontaken in conjunction with the drawings.

FIG. I is a vertical view partly in section and partly schematic of thelower part of a well penetrating an underground producing formation.

FIG. 2 is a vertical view partly in section and partly schematic of awell penetrating an underground producing formation and including meansfor injecting a liquid explosive in such well.

FIG. 3 is similar to FIG. 1 except it illustrates the well after liquidexplosive has been placed therein.

FIG. 4 is a cross section showing details of a fill-up collar and a pluglatched therein.

FIG. 5 is a cross section of a shear plug sub with a plug in lace. pFIG. 6 shows a detonator with a specially modified housing.

DETAILED DESCRIPTION OF THE INVENTION Attention is first directed toFIG. 1 which shows a well bore 10 which penetrates a producing formation12. An upper part of the borehole 10 is cased' with casing 14 cementedin place in a conventional manner. In this particular case, casing 14does not extend through producing formation 12. FIG. I is merely thelower end of well 10 and illustrates the first equipment which is placedin the well bore in the carrying out of the process of this invention. Adrillable packer I6 is set in the casing just above producing formation12. Drillable packer 16 is of a character which has a vertical passagetherethrough and which is adapted to receive a tubing with seal nippleso as to form a continuous conduit with a tubing string. Suspendedbeneath the drillable packer 16 is a first section 18 of a drillabletubing such as aluminum tubing and can be for example about l0 feetlong. Connected to the lower end of tubing 18 is a fill-up collar withplug latch 20. Details of this are shown in the cross section view ofFIG. 4. Immediately beneath the fillup collar 20 is a shear plug sub 22.The details of this type sub are shown in FIG. 5. Immediately belowshear plug 22 is a drillable tail tubing 24 which can for example beabout 30 feet long.

A detonator 26 is shown in the bottom of the well 10 and was placedthere with wire line prior to the setting of drillable packer I6 and itsassociated equipment. This bomb or detonator is a clocked detonator andis set to detonate at a time after the explosive and other operationalsteps have been taken, for example, it can be set to detonate in 48hours.

Attention is next directed to FIG. 2 which illustrates a tubing 25suspended in the well bore above packer 16. It also illustrates meansfor displacing the liquid explosive into the tubing.

A pipeline 29 having valve 30 therein connects the annulus 31 of thewell bore with a pit or tank not shown. THis is used when displacing afluid such as cement slurry into the casing 14 above packer I6.

Attention will now be directed briefly toward that part of the equipmentlocated on the surface which is used for injecting the liquid explosiveinto the well bore. This includes a container or source 34 having anexplosive slurry or liquid therein. A nitrogen source 36 is connectedthrough line 38 having valve 40 to drive the liquid explosive fromcontainer 34. The outlet of container 34 is connected through line 42 toa well head manifold 49. Line 42 has a valve 48 adjacent container 34.The outlet of pump 44 is connected through line 46 to tubing string 25through manifold 49. Pump 44 is high-pressure pump such as a triplexplunger positive displacement pump. A sorbing solvent source indicatedas container 50 is provided. This has an outlet line 52 which connectsinto line 64 leading to pump 44. Line 52 has a valve 54 therein adjacentcontainer 50. A water source 62 connects through conduit 67 having valve66 to conduit 64. Conduit 64 is connected to pump 44. A packing gland 58is in the upper end of tubing string 25 to be used in event it isdesired to run a wire line into the well. A lower plug 32 and top plug35 are held in position by suitable catches 33 and 27 respectively. Plug32 will pass through fill-up collar 20. However, this fill-up collarwill retain top plug 35. The operational reasons for this will becomeapparent.

OPERATION SYSTEM In one embodiment of this operation, detonator 26 isfirst placed in the hole as shown in FIG. I. Then the liquid explo siveis injected. When we first inject the liquid explosive, tubing string 25is suspended as shown in FIG. 2. That is, the lower end of tubing 25 isabove packer 16. In this system the liquid explosive is injected downthe tubing 25 and the well liquid is taken out through pipe 29 from theannulus. It was taught in copending application Ser. No. 875,843, filedNov. 12, 1969, for Clarence R. Fast, George C. Howard and Morton A.Mallinger and assigned to a common assignee with this application, thatit is sometimes desirable to use a sorbing solvent to prevent theformation of mixtures of air vapors, etc., adjacent the liquid explosivewhich when compressed gases, etc., can cause liquid explosive to igniteor detonate prematurely. As taught in that application a suitablesorbing solvent is one that desensitizes the explosives and, therefore,can be,

for example, dibutyl phthalate, toluene, benzene or the like fornitromethane base explosives.

Valves 72 and 54 are open (valves 68, 48 and 66 are closed) so that asorbing solvent from container 50 can be pumped into the tubing 25 justbelow bottom plug 32. Then valve 72 is closed and valve 70 opened. Thenthe sorbing solvent is injected into the tubing extension through valve70 on top of plug 32. Plug 32 fits rather closely in tubing 25 but canpas through fill-up collar 20. Valves 72 and 68 are closed. Valves 70,48 and 40 are open and plug catch 33 released so that nitrogen may forceexplosive liquid through container 34, through line 42 into tubing 25 ontop of plug 32 which will move down tubing string 25. Tubing 25 willordinarily have sufficient capacity so that the desired quantity ofexplosive liquid can be displaced so that the top of the explosive iswell below ground level. At this time valves 40, 48 and 70 are closed.The desired amount of liquid explosive will have been preselected andordinarily may be typically in the range of 500 to 2,000 gallons. Afterthe selected amount of explosive is injected into the tubing, valve 48is closed and valve 54 is open so that a sorbing solvent can be placednext to the top of the liquid explosive. When the desired amount ofsorbing solvent has been injected valves 54 and 70 are closed and valves66 and 68 open. This is to permit the pumping of water on top of plug 35so that the top plug and the explosive can be displaced further into thetubing. Catch 27 is then released. This displacement by water continuesuntil the liquid explosive approaches the lower end of tubing 25. Thiscan be determined by simple volumetric calculations. At this pointtubing 25 is lowered into and fastened into packer 16. The only thingnow which prevents a continuous conduit from being formed from thesurface to well bore opposite formation 12 is the plug in shear plug sub22. This plug is axially removed simply by applying additional pressureto the liquid in tubing 25. This pressure is applied until shear pin 101(shown in FIG. 5) is sheared. This permits plug 102 to be forceddownwardly through tubing tail pipe 24. It will be noted that shear plug102 has sealing means 103 so that while the plug is in place it forms aseal.

Now it is seen then there is a continuous conduit formed from thesurface through tubing 25, packer l6 and tail pipe 24 with the well boreopposite formation 12. Water is continued to be pumped through thetubing forcing the liquid explosive on down into tail pipe 24. Lowerplug 32 is a conventional ce menting wiper plug with a soft outerelastomer body having a hard metal or plastic core. The plug is designedto wipe the pipe walls clean as it moves down the tubing. The dimensionsof plug 32 are such that the plug will pass through fill-up collar 20,shear plug sub 22 and tail pipe 24.

Top plug 35, sub 20 and plug latching means 21 are shown in detail inFIG. 4. Latching means 21 is simply a reduced diameter ring that isfitted in the sub 20. Top plug 35 consists of elastomer wiper portions82 and 84 connected by solid center portion 86. The dimension of centerportion 86 are such that the bottom part 88 of the center portion 86 ofplug 35 will pass through latching means 21. The top part 90 of centerportion 86 of plug 35 is preferably a solid, essentially nondeformablering which will not pass through latching means 21. The plug 35 alsocontains latching rings 92 which is a split ring that compresses onpassing through latching means 21 and expands after passing through sothat latching ring 92 bears against shoulder 94, thereby locking plug 35in place so that it cannot move upward. Top part 90 of the plug preventsdownward movement. Top plug 35 and catcher 21 are commercially availablefrom Baker Oil Tools, Inc., Los Angeles, Cal., and are identified asModel C cementing plug and full flow fill-up collar. This particularcommercially available equipment contains a steel top part 90 and steellatching means 21 and latching rings 92. These parts could also be madeof plastic material.

Water is continued to be pumped until top plug 35 is securely latchedinto latch means 21. This is easily determined both by volumetriccalculations and by the fact that when plug 35 is latched in place, thepump pressure on tubing 25 will show an abrupt increase. This lets usknow that all the explosive is in the well bore or tail pipe 24 beneathpacker l6. Tubing string 25 is then disconnected from packer l6 and ispartially removed from the well bore or tract. Sufficient tubing isremoved so that the lower end is sufficiently removed from the packer 16so that when the explosive is detonated the tubing will not be damaged.Before the time for the detonation to occur, the well is stemmed. Abovepacker I6 is cement 74. It has been found that about 100 feet of cementwould ordinarily be adequate. Above the cement, sand has been placed andextends about 200 feet up into the casing. The remainder of the hole isfilled with water to the surface. When the time set on the timed bomb 26has elapsed, it ignites or detonates the explosive in the well borecausing shattering and fracturing of the rock immediately surroundingthe well bore. After this has occurred the well bore is cleaned outusing conventional equipment in a conventional manner. The well is thensubsequently placed on production, also in a conventional manner.

While the above described operation is a preferred way of using ourinvention, it can be modified. For example if the particular liquidexplosive used is not particularly heat sensitive, then it is notnecessary to inject the sorbing solvent.

Other modifications include different ways of igniting the liquidexplosive placed in the well bore below packer 16. In the systemdescribed above we place the time bomb or detonator 26 in the bottom ofthe well prior to the other operations. The above described system ofplacing the detonator in the well bore first has a possible disadvantagethat the detonator is in the bottom of the well during the injection ofthe explosive. We can modify this procedure by the use of the detonatoras shown in FIG. 6. In this modified procedure, detonator 26 is notplaced in the well bore prior to injecting the liquid explosive. Rather,the liquid explosive is injected into tubing 25. Then, just beforeinserting top plug 35, the special detonator of FIG. 6 is inserted by aspecial lubricator. The special drop-type detonator shown in FIG. 6 isdesigned to fall slowly through the liquid explosive and the sub. Thisis accomplished by providing a rubber wiper plug 107 on top to cause theplug to move slowly through the liquid explosive. The top of the bombalso contains fishing neck 109 to facilitate the bomb removal from thetubing should this become necessary. The bomb is designed so that itscasing can withstand the pressure required to inject the explosive. Itis shown to have a rounded or cone-shaped nose and is preferablyconstructed of a drillable material which is partly cast iron oraluminum. The bomb inside this casing contains standard timingmechanisms with electric blasting caps and suitable detonators.

There are many suitable liquid explosives which can be used. One typeliquid explosive is one in which nitromethane is the predominantcomposition and contains a thickening agent, sensitizer and otheradditives tailored to the bottomhole temperatures, pressure and typeformation. A suitable commercially available liquid explosive isTAL-IOOS which is available from Talley Industries, Inc., Mesa, Arizona.

While the above embodiments of the invention have been described withconsiderable detail it is to be understood that various modifications ofthe device can be made without departing from the spirit or the scope ofthe invention.

We claim:

1. A method of stimulating a well by the use of a liquid explosive whichcomprises:

placing a timed detonator in the vicinity of the bottom of the well;providing a drillable packer fitted with a plug catcher sub and a subcontaining a pumpout blanking plug and setting said packer above theformation to be stimulated;

equipping a tubing string with a special locator tubing seal nipple nearthe bottom end;

running said tubing string in said well bore until said seal nipple is afew feet above the packer;

filling the well above the packer with a first liquid;

displacing the liquid explosive into the tubing while removing saidfirst liquid from the well and the tubing until the desired amount ofliquid explosive is injected into the tubing string;

thereafter connecting the tubing string to the packer;

then applying sufficient pressure to the tubing string to pump out theblanking plug;

then displacing the liquid explosive out of the tubing string into thewell bore below the packer;

setting a plug in the plug-catcher sub;

stemming the well above the packer;

detonating the explosive;

after detonation of the explosive, cleaning out the well so that it maybe placed on production.

2. A method as defined in claim 1 in which a rubber bottom plug isplaced between said liquid and said liquid explosive.

3. A method as defined in claim 1 in which prior to said stemming, saidtubing string is disconnected from said packer and withdrawn from thevicinity of said packer and in which said stemming includes placing saidcement above the packer.

4. A method as defined in claim 1 including the step of attaching adrillable section of tubing below said packer with its lower end abovethe bottom of said well so that said liquid explosive can be displacedout the lower end of said drillable section of tubing.

5. A method of stimulating a well by the use of a liquid explosive whichcomprises:

setting a plug in said well above the formation to be stimulated;

running a tubing string with the lower end just above said forcing saidliquid explosive into said tubing string until the desired amount isinjected therein;

then forming a continuous conduit from the lower end of said tubing tobelow said plug;

forcing said liquid explosive from said tubing string through saidcontinuous conduit to the well below said plug; sealing said continuousconduit;

detonating said liquid explosive.

6. A method as defined in claim 5 including the step of removing saidtubing string from the vicinity of said plug and stemming said wellprior to said step of detonating said liquid explosive.

7. A method as defined in claim 6 in which the step of detonating saidliquid explosive is accomplished by placing a timed detonator in thebottom of said well prior to the injection of said liquid explosive.

8. A method as defined in claim 6 in which the step of detonating saidliquid is accomplished by dropping a detonator through said liquidexplosive through said tubing string and said continuous conduit priorto the sealing of said continuous conduit.

9. A method as defined in claim 6 including the step of removing saidtubing string from the vicinity of said plug, filling said well withliquid prior to said step of detonating said liquid explosive.

10. A method of stimulating a well by the use of a liquid explosivewhich comprises:

setting a packer in said well above the formation to be stimulated;

running a tubing string with the lower end just above said detonatinsaid liquid ex losive. 11. A met od as define in claim 10 including thesteps of removing said tubing string from the vicinity of said packerand stemming said well prior to said step of detonating said liquidexplosive.

12. A method of stimulating a well by the use of a liquid explosivewhich comprises:

providing a drillable packer fitted with a plug catcher sub and settingsaid packer above the formation to be stimulated;

equipping a tubing string with a special locator tubing seal nipple nearthe bottom and;

running said tubing string in said well bore until said seal nipple is afew feet above the packer;

filling the well above the packer with a first nonexplosive liquid;

forcing liquid explosive into the tubing until the desired amount ofliquid explosive is injected into the tubing string;

thereafter connecting the tubing string to the packer;

retaining the liquid explosive in said tubing string until it isconnected to the packer;

displacing the liquid explosive out of the tubing string into the wellbore below the packer:

setting a plug in the plug catcher sub; and

detonating the explosive.

13. A method as defined in claim 12 including the steps of disconnectingthe tubing string from the packer and removing it from the vicinity ofthe packer and stemming the well above the packer.

14. A method of stimulating a well by the use of a liquid explosivewhich comprises:

[5. A method as defined in claim 14 including the steps of removing saidtubing string from the vicinity of said packer and stemming said wallprior to said step of detonating said liquid explosive.

2. A method as defined in claim 1 in which a rubber bottom plug isplaced between said liquid and said liquid explosive.
 3. A method asdefined in claim 1 in which prior to said stemming, said tubing stringis disconnected from said packer and withdrawn from the vicinity of saidpacker and in which said stemming includes placing said cement above thepacker.
 4. A method as defined in claim 1 including the step ofattaching a drillable section of tubing below said packer with its lowerend above the bottom of said well so that said liquid explosive can bedisplaced out the lower end of said drillable section of tubing.
 5. Amethod of stimulating a well by the use of a liquid explosive whichcomprises: setting a plug in said well above the formation to bestimulated; running a tubing string with the lower end just above saidplug; forcing said liquid explosive into said tubing string until thedesired amount is injected therein; then forming a continuous conduitfrom the lower end of said tubing to below said plug; forcing saidliquid explosive from said tubing string through said continuous conduitto the well below said plug; sealing said continuous conduit; detonatingsaid liquid explosive.
 6. A method as defined in claim 5 including thestep of removing said tubing string from the vicinity of said plug andstemming said well Prior to said step of detonating said liquidexplosive.
 7. A method as defined in claim 6 in which the step ofdetonating said liquid explosive is accomplished by placing a timeddetonator in the bottom of said well prior to the injection of saidliquid explosive.
 8. A method as defined in claim 6 in which the step ofdetonating said liquid is accomplished by dropping a detonator throughsaid liquid explosive through said tubing string and said continuousconduit prior to the sealing of said continuous conduit.
 9. A method asdefined in claim 6 including the step of removing said tubing stringfrom the vicinity of said plug, filling said well with liquid prior tosaid step of detonating said liquid explosive.
 10. A method ofstimulating a well by the use of a liquid explosive which comprises:setting a packer in said well above the formation to be stimulated;running a tubing string with the lower end just above said packer;forcing said liquid explosive into said tubing string until the desiredamount is injected therein; connecting the lower end of said tubingstring into said packer to form a continuous passage from said tubing tobelow said packer; forcing said liquid explosive from said tubing stringto the well below said packer; sealing the passage through said packerso that the well bore below said packer is isolated from the well boreabove; and detonating said liquid explosive.
 11. A method as defined inclaim 10 including the steps of removing said tubing string from thevicinity of said packer and stemming said well prior to said step ofdetonating said liquid explosive.
 12. A method of stimulating a well bythe use of a liquid explosive which comprises: providing a drillablepacker fitted with a plug catcher sub and setting said packer above theformation to be stimulated; equipping a tubing string with a speciallocator tubing seal nipple near the bottom and; running said tubingstring in said well bore until said seal nipple is a few feet above thepacker; filling the well above the packer with a first nonexplosiveliquid; forcing liquid explosive into the tubing until the desiredamount of liquid explosive is injected into the tubing string;thereafter connecting the tubing string to the packer; retaining theliquid explosive in said tubing string until it is connected to thepacker; displacing the liquid explosive out of the tubing string intothe well bore below the packer; setting a plug in the plug catcher sub;and detonating the explosive.
 13. A method as defined in claim 12including the steps of disconnecting the tubing string from the packerand removing it from the vicinity of the packer and stemming the wellabove the packer.
 14. A method of stimulating a well by the use of aliquid explosive which comprises: setting a packer in said well abovethe formation to be stimulated; thereafter running a tubing string andlatching same into the packer; forming a continuous passage from saidtubing to below said packer; forcing said liquid explosive into saidtubing string until the desired amount is injected therein; forcing saidliquid explosive from said tubing string to the well below said packer;sealing the passage through said packer so that the well bore below saidpacker is isolated from the well bore above; and detonating said liquidexplosive.
 15. A method as defined in claim 14 including the steps ofremoving said tubing string from the vicinity of said packer andstemming said well prior to said step of detonating said liquidexplosive.